The present invention relates to an apparatus that inspects the critical dimensions of fine patterns formed on a sample using a charged particle beam, and more particularly to a charged particle beam application technique for use in an inspection apparatus for semiconductors, for example.
In manufacture of a semiconductor device, for example, since micro circuit patterns are formed in many layers, inspection is performed whether patterns are processed as designed or whether the critical dimensions of patterns are not varied. For this pattern inspection, a scanning electron microscope (SEM) suited to the inspection of the critical dimensions of fine patterns is widely used. In the SEM, an inspection sample is scanned while applying an electron beam to the sample, signal electrons (secondary electrons and back scattered electrons) emitted from the inspection sample are detected, and a scan image (a so-called SEM image) is obtained.
The SEM for use in the critical dimension management of inspection in manufacture is demanded to continuously operate for a long time, and it is necessary to continuously supply electrons applied to a sample in order to continuously operate the apparatus. To this end, a surface diffusion electron source is practically used, in which a single crystal tip is made of a high melting point metal material such as W and Mo and a metal whose work function is lower than the work function of a single crystal tip such as an oxide or a nitride of Zr, Ti, Sc, Hf, or Ba is adsorbed into the surface of the single crystal tip in the order of a monatomic layer. An electric current is carried through a filament to heat such an electron source at a high temperature of 1,500 to 1,900 K, a strong electric field of 5×108 to 1.5×109 V/m is applied, and a stable emission is implemented. Such an electron source is called a Schottky emitter. In the following, in the present specification, the Schottky emitter is noted as an SE tip or simply an electron source.
In a typical electron microscope, the diameter of an electron beam emitted from an electron source is reduced using an aperture formed on a diaphragm, and a part of the beam is applied to a sample. For example, related art literature related to this technique include Japanese Patent Application Laid-Open Publication No. Hei-07-094134, Japanese Patent Application Laid-Open Publication No. Hei-08-222163, M. S. Bronsgeest, P. Kruit, Ultramicroscopy, 110, pp. 1243-1254 (2010), and Orloff, Handbook of Charged Particle Optics, Press, New york (1997).